Microemulsions are known in the art. They are stable isotropic mixtures of oil, water, and surfactant which form spontaneously upon contact of the ingredients. Other components, such as salt or co-surfactant (an alcohol, amine, or other amphiphilic molecule) may also be part of the microemulsion formulation. The oil and water reside in distinct domains separated by an interfacial layer rich in surfactant. Because the domains of oil or water are small, microemulsions appear visually transparent or translucent. Unlike emulsions, microemulsions are equilibrium phases.
Microemulsions can have a variety of microstructures, depending mainly upon composition and temperature. The common structural feature is the presence of a surfactantodch sheet or film separating oil-rich and water-rich domains. There are three most common structures. One is the so-called water-in-oil microemulsions, in which water is contained inside distinct domains (droplets) in a continuous oil-dch domain. A second is oil-in-water microemulsions in which oil is contained inside distinct domains in a continuous water-rich domain. The third is bicontinuous microemulsions in which there are sample-spanning intertwined paths of both oil and water, separated from each other by the surfactant-rich film (a sponge-like structure).
A microemulsion can be distinguished from a conventional emulsion by its optical clarity, low viscosity, small domain size, thermodynamic stability, and spontaneous formation. Microemulsion polymerization has several advantages over traditional emulsion polymerization. First, emulsions are turbid and opaque, while microemulsions are usually transparent or translucent and so are particularly suitable for photochemical reactions. Second, microemulsion polymerization enables preparation of stable, monodispersed colloidal dispersions containing particles that are smaller than particles produced with classical emulsion polymerization processes. Finally, the structural diversity of microemulsions (droplet and bicontinuous) is set by thermodynamics, and rapid polymerization may be able to capture some of the original structure.
Coating substrates with fluorinated polymers is known in the art. In order to produce a thin uniform coating, such processes normally require expensive and/or environmental-hazardous fluorinated solvents, such as CFCs. Moreover, water-based emulsion polymerization of fluorinated monomers usually yields particles with size in the range of 0.1-10 micrometer, which sometimes makes it difficult to give uniform coatings on porous substrates having submicron pore structures. In addition, such large particle sizes result in coatings that can clog the pores of submicron pore structures, which is undesirable in many applications.
Fluoropolymers containing tetrafluoroethylene generally have superior thermal stability to other polymers. It would be desirable to provide new microemulsions polymerization technique involving tetrafluoroethylene to produce polymers of very small particle sizes. It would also be desirable to provide coated substrates in which the coatings are made from the small polymer particles.